Thermally stabilized electronic assembly



April 8,' 1969 I 3,437,789 7 THERMALLY STABILIZED ELECTRONIC ASSEMBLY I I Filed Sept. 28, 1966 R. CHARBONNIER ET AL Sheet April 8, 1969 QHARBONNIER ET AL THERMALLY- STABILIZED ELECTRONIC ASSEMBLY Filed Sept. 28, 1966 Sheet -Roger Charbonnier, 15 Rue Emile,

United States Patent 3,437,789 THERMALLY STABILIZED ELECTRONIC ASSEMBLY Meudon 92, France,

and Jean Royer, 22 bis Par de Montretout, Saint- Cloud 75, France Filed Sept. 28, 1966, Ser. No. 582,662 Claims priority, application France, Oct. 7, 1965, 34,127 Int. Cl. Hb 1/02, 11/00 U.S. Cl. 219209 2 Claims This invention relates to thermally-stabilized assemblies and, more particularly, to electronic circuit assemblies in which the respective components are thermally stabilized.

In the copending application Ser. No. 470,161, filed on July 7, 1965, now Patent No. 3,387,113, for Electronic Assembly, there is disclosed the use, for thermal regulation, of a new thermosensitive element, the temperature coeificient of which is positive and very high. A thermosensitive element of this type is known under the trade name of Resistance C.T.P. E.220ZZ/03. It is manufactured in Belgium by Manufacture Belge de Lampes Electriques.

The thermosensitive elements of this type are characterized by a known, relative-linear variation of resistance with temperature. However, the variation of resistance is very abrupt around a critical reference temperature which can be made to depend on the chemical composition of the thermosensitive element. A critical reference temperature within the range of 30 C. and 120 C. is quite normal. In the illustrated applications subsequently described, the critical reference temperature is approximatively 80 C. The rate of variation of resistance can also be changed by controlling the composition of the materials used. The rate can vary between and 90% per degree Centigrade. The thermosensitive elements are made of various compositions according to the value of the desired critical reference temperature and the extent of the range of regulation. In general, the thermosensitive element is a ceramic made from a ferroelectric material doped with a small quantity of one or two metal modifiers of convenient valence subsequently fritted at a carefully chosen temperature. Among the different families of useable ferroelectric materials, those selected are the Perovskites such as BaTiO mixed titanates of barium and strontium (Ba, Sr) TiO mixed titanates of barium and lead (Ba, Pb) TiO mixed tantalates of sodium and potassium (Na, K) TaO or niobiate of potassium KNbO It will be noted that the conditions of fritting of the Perovskites are preferably so deter-mined that the amount of oxygen in the ceramic obtained should be stoichiometric. Among the metal modifiers whichcan be associated according to their valence with the above Perovs'kites, it is desirable to use antimony, tungsten, niobium, zirconium, yttrium, cerium, and lanthanum. This list is obviously not limitative and all compositions which present a rapid growth of electric resistance in a range of one side and the other of a critical reference temperature can be used for the realization of an electronic component with individual thermal regulation in accordance with the object of the present invention.

When to such a thermosensitive element is applied a substantially constant voltage, it can present in the neighborhood of its critical temperature a rapid diminution in the consumed power. To a first approximation, this phenomenon can be compared to a thermal discontinuity. Hence, this sudden diminution in the consumed power makes it possible to use the thermosensitive element as a temperature sensor, a reference comparator, an amplifier, and an active component.

More specifically, in the copending application above referred to, there is disclosed an electronic assembly of the type comprising at least one circuit element mounted on a support of heat-sensitive material which produces a rapid increase in electrical resistance over a so-called regulation range which is located on each side of a critical reference temperature, said support and said element being interconnected by means of electric current conductors comprising connector-pins mounted in a base, characterized in that said heat-sensitive support, preferably presented in the form of a pastille, both faces of which are metallized and connected to two of said conductors, has one of said faces or so-called hot face being adapted to carry said circuit element and connected to the surrounding atmosphere through a high-value parasitic thermal resistance whilst the other face or so-called cold face is connected to the surrounding atmosphere through a thermal resistance having a value which is small with respect to the preceding resistance. This type of electronic assembly will be referred to hereinafter as an electronic assembly of the type defined.

In the copending application referred to above, there was also described a particular embodiment of the invention in which the cold face of the heat-sensitive pastille was in contact with an insulating plate secured to the base of the component. This embodiment makes it possible to obtain a regulation of the characteristics of electronic components which satisfies the majority of commercial requirements. However, a more extensive study of the operation of this embodiment has shown that, in a few special cases, such an arrangement was attended by certain disadvantages.

In particular, some temperature differences may appear, in this embodiment, between the terminals of the electronic circuit elements to be regulated, which is a major drawback, especially in the case of semiconductor circuits elements to be regulated, which is a major drawback, especially in the case of semiconductor circuits. Another cause of disturbance in the circuits will consist in the variable potential differences which may appear at some points of the conductors where two different metals generally are welded.

It is an object of the present invention to provide a modified embodiment of the electronic assembly disclosed in the previously discussed copending application, which is free of the above drawbacks.

It is another object of the present invention to provide an electronic assembly of the type defined, wherein the thermal flux within the conductors which are connected to the terminals of the circuit component which it is desired to regulate is decreased to a considerable extent.

Yet a further object of this invention is to provide an electronic assembly of the type defined, wherein the cold face of said heat-sensitive support is fixed to an electrically insulating and heat-conducting plate which is mounted at the ends of said connector-pins, substantially parallel to said base, said connector-pins thus forming support columns for said plate.

These and other objects of the invention will become apparent from the following description, reference being had to the accompanying drawings, in which:

FIG. 1 is a sectional diagrammatic view of an electronic assembly of the type specified, as disclosed in the previously discussed copending application;

FIG. 2 is a circuit diagram which includes the thermal resistances in the electronic assembly illustrated in FIG. 1;

FIG. 3 is a sectional diagram of the new arrangement in accordance with the present invention;

FIG. 4 is a circuit diagram which includes the thermal resistances in the electronic assembly illustrtaed in FIG. 3 and FIG. 5 illustrates in perspective an exemplified embodiment of a temperature-regulated electronic assembly built in accordance with the present invention.

Before starting the description of the electronic assembly in accordance with this invention, reference will be had to FIGS. 1 and 2, with a view to illustrate the operation of the embodiment of the electronic assembly of the type specified which is disclosed in the previously discussed copending application.

According to FIG. 1 a circuit element E, for instance a transistor, is in thermal Contact with the top face of a heat-sensitive pastille T, the underface of which is secured to an insulating plate P which is in turn fixed to the base S of the component. The connector-pin C is mounted across the base S and connected at point B to the connecting wire F which joins the terminal A of the circuit element E.

It is to be understood that there are a plurality of such connector-pins and wires, which need not be shown in the diagram of FIG. 1 but connect the terminals of circuit element E and the faces of pastille T to external circuits, not illustrated.

FIG. 2 illustrates the connections between the thermal resistances which exist in the device of FIG. 1, the base S constituting the ground potential. Between the point A and ground are disposed the thermal resistance R of the plate P and the thermal resistance R of the heat-sensitive pastille T and of the circuit element E. The thermal flux I which is produced by the heat-sensitive pastille T when the said pastille is energized from the supply voltage from external circuits is developed in a hot region in the interior of said pastille T. It may be shown that the hot region to which the thermal fiux I is thus applied is separated from the point A by a first thermal resistance R and from its underface by a second thermal resistance R with R R There is developed between all of the points A and all of the points B which correspond to the various connecting wires and pins a thermal resistance R which is constituted by the complete assembly of connecting wires F. Between all of the points B and ground, there appears a thermal resistance R; which is constituted by the different connector-pins C.

It may be shown that the thermal resistances R and R will generally have the same order of magnitude (approximately 40 C./w.) whereas the sum of the thermal resistances R and R will be of the order of 1,000 C./w. It can therefore be considered as a. first approximation that the thermal potential V at the point A is equal to I(R -l-R Moreover, since R is small compared with R the thermal flux within all of the Conductors F is V /R Said thermal flux is high and produces a thermal gradient within the mass of the circuit element E to be temperature-regulated which is not negligible. In as much as the different conductors F which interconnect the various terminals of the circuit elements E to the pins C have different lengths, the thermal flux within each of said conductors is different. As a consequence, not-negligible temperature differences will appear between the terminals of the circuit elements to be regulated.

Furthermore, as a result of the different thermal fluxes which pass through them, the different extremities B of the connector-pins C are accordingly heated to different temperatures. Since the points B usually consist of welded junctions formed of two different metals (gold wires in the case of the conductors F and Kovar in the case of the connector-pins C, for example) thermocouples are created and develop potential diferences which vary from one point B to the other. This is a further cause of disturbance in the circuits which it is desired to regulate.

Referring now to FIG. 3 which shows diagrammatically the arrangement in accordance with the invention, the heat-sensitive pastille T is fixed to an electrically-insulating and heat-conducting plate D which is supported on small columns constituted b the connector-pins C of 4 the component. All of the remaining elements shown are identical with the corresponding elements of FIG. 1.

FIG. 4 represents the electrical analogy of the thermal resistances employed in FIG. 3 and shows that, in this new form of construction, the thermal resistance R is connected between the points A and B whilst the thermal leak resistance which is connected to the cold face of the heat-sensitive pastille T is represented by R' It has been shown in the previously discussed copending application that a thermal resistance of relatively small value must be interposed between the base of the assembly and the cold face of the heat-sensitive pastille. In the embodiment of FIG. 3, this thermal resistance is constituted by connecting the different connector-pins C in parallel. Consequently, the value of said thermal resistance will be known with accuracy. Under these conditions, the temperature of the points B to which the connecting wires F are joined is appreciably higher than the temperature which prevailed in the embodiment of my copending application. It follows as a result that, along the connecting wires F which join the terminals A of the circuit element to be regulated to the extremities B of the connector-pins, a small thermal potential difference is established which, in addition, is identical from one connector to the other. Under these conditions, the parasitic thermal resistance which is constituted by the wires F which serve to connect the circuit element E to the hot face of the heat-sensitivepastille T is in parallel only with the thermal resistance of said pastille and no longer, as in the embodiment of my copending application, with the thermal resistance of the heat-sensitive pastille and of the insulating plate which is fixed to the base. It results that the influence of said parasitic thermal resistance is considerably decreased.

The properties and advantages of the invention will in any case become more readily apparent from the description of the electronic assembly illustrated in FIG. 5. In this figure, the reference 50 designates a metal base mounted on an annular flange 52 over which the component cover (not shown) is intended to be fitted. The base 50 is provided for example with eight insulating lead-in bushings such as the bushing 53 whereby eight connector-pins 54 68 are mounted in the base 50. A ceramic plate 70 is attached to the extremities of the connector-pins 54 68 which constitute small columns for supporting said plate 70. There are disposed on the top face of the plate 70 seven metallic sectors 55 67 whilst the underface of said plate 70 is metallized by means of a metal film which is connected to the extremity of the connector-pin 68. There is welded to said metal film the top face of a heat-sensitive pastille 72 formed of a material which exhibits a rapid increase in electrical resistance over a regulation range which is located on each side of a critical reference temperature. The underface of the pastille 72 is metallized and welded to a disc 74 which possesses good heat conductivity and good electrical insulation properties. In addition, the underface of said pastille 72 is connected by means of a conductor 76 to the metal sector 55 which is welded to the extremity of the connector-pin 54. The underface of the disc 74 is metallized and carries a pair of transistors such as the transistor 78. The three terminals of the transistor 78 are respectively connected by means of the conductors 80, 82 and 84 to the connectorpins 56, 58 and 60 which are respectively welded to the metal sectors 57, 59 and 61 of the top faces of the plate 70.

The practical advantage of a component as shown in FIG. 5 will be immediately evident when consideration is given to the diagram of thermal resistances of said component as shown in FIG. 4. The component is of special interest in the case of low-power transistors which are employed, for example, for the purpose of forming the first stage of an amplifier In fact, in such a case, the power which is really dissipated in the two transistors of a differential input amplifier is mw. at a maximum. If the minimum power which is dissipated within the heat-sensitive pastille 72 (or the pastille T in FIG. 3) is 90 mw., a minimum power of 100 mw. is accordingly dissipated within said pastille. If it is assumed, for example, that the difference between the top temperature limit of the range of regulation of the heatsensitive pastille T and the maximum ambient temperature is 30 C., we therefore have as maximum value of the thermal resistance R (FIG. 2) or R (FIG. 4):300 C./w. If we assume by way of example that R =R' -=270 C./W. and R =30 C./w. in the devices which are shown diagrammatically in FIGS. 2 and 4, we have between the points A and B a thermal potential ditference:V V =10(V V In other words, in the case of FIGS. 3 and 4, the thermal gradients within the conductors F and especially within the transistors E are ten times lower than in the case of FIGS. 1 and 2.

The practical value of the new form of construction in accordance with the present invention will therefore be readily apparent from the specific example which has just been given as an illustration only.

It must be added that the material which constitutes the plate 70 of FIG. 3 has good heat conductivity and therefore that said plate can be considered as isothermal. Under these conditions, it can be stated definitely that the different thermocouples which are constituted by the welded junctions of the connector-pins 56 64 and the connecting wires such as 80, 82 and 84 are at a same temperature and therefore give rise to a same potential difference. The result thereby achieved is that the parasitic voltage sources which were created by the temperature differences observed in the first embodiment at the extremities of the connector-pins of the component are accordingly eliminated in the new embodiment which is contemplated in the present invention.

A further appreciable advantage of the present embodiment lies in the ease of construction of a component in accordance with FIG. 5. In fact, in order to manufacture said component on an industrial scale, it is a very simple matter to fix the pastille 72 on the plate 70, then to fix the transistors 78 on the underface of said pastille, in such a manner as to constitute a subassembly which can subsequently be mounted without difficulty on the connector-pins 54 68 of a base 50. I

As will be readily understood, the invention is not limited to the embodiment of FIG. 5. For example, it will be noted that, in order to attach the conductors 80, 82 and 84 at the extremities of the connector-pins '56, 58 and 60 to the sectors 57, 59 and 61, a mode of attachment by flattening or swagging could readily be adopted in the place of welding.

What is claimed is:

1. An electronic assembly comprising: a base; at least one circuit component; a support of thermosensitive material presenting a rapid increase of electric resistance in a range of regulation situated on both sides of a critical reference temperature, said support having first and second faces, said first face being in thermal contact with said circuit component; a plurality of electric current conductors mounted on the periphery of said base, said conductors having rigid portions of substantially the same length on one side of said base, substantially at right angles to the surface thereof, a thermally conductive plate of electrically insulating material mounted at the ends of said rigid portions substantially parallel to said base, said plate being in thermal contact with said second face, and means connecting said circuit component and the first and second faces of said thermosensitive support to said electric current conductors, said first face being coupled to the ambient temperature through a first thermal resistance, said second face being coupled to the ambient temperature through a second thermal resistance, said first thermal resistance being substantially larger than said second thermal resistance.

2. An electronic assembly as claimed in claim 1, wherein the faces of said thermosensitive support are metallized, said plate being a ceramic dis having first and second faces, the second face of said disc being metallized and welded to the second face of said thermosensitive support and the first face of said disc having a metallized portion and a nonmetallized portion, said plurality of rigid conductor portions including a first conductor portion in contact with the nonmetallized portion of said first face and with said second metallized face of said disc, a second conductor portion in contact with a first metallized portion of said first face and a plurality of further conductor portions respectively in contact with further metallized portion-s of said first face, the said means connecting said first metallized portion to the first metallized face of said thermosensitive support and said further metallized portions to said electric component.

References Cited UNITED STATES PATENTS 6/1962 Wolfskill 219210 6/1968 Charbonnier 2l9209 US. Cl. X.R. 2l9501, 510; 3l7235 

1. AN ELECTRONIC ASSEMBLY COMPRISING: A BASE; AT LEAST ONE CIRCUIT COMPONENT; A SUPPORT OF THERMOSENSITIVE MATERIAL PRESENTING A RAPID INCREASE OF ELECTRIC RESISTANCE IN A RANGE OF REGULATION SITUATED ON BOTH SIDES OF A CRITICAL REFERENCE TEMPERATURE, SAID SUPPORT HAVING FIRST AND SECOND FACES, SAID FIRST FACE BEING IN THERMAL CONTACT WITH SAID CIRCUIT COMPONENT; A PLURALITY OF ELECTRIC CURRENT CONDUCTORS MOUNTED ON THE PERIPHERY OF SAID BASE, SAID CONDUCTORS HAVING RIGID PORTIONS OF SUBSTANTIALLY THE SAME LENGTH ON ONE SIDE OF SAID BASE, SUBSTANTIALLY AT RIGHT ANGLES TO THE SURFACE THEREOF, A THERMALLY CONDUCTIVE PLATE OF ELECTRICALLY INSULATING MATERIAL MOUNTED AT THE ENDS OF SAID RIGID PORTIONS SUBSTANTIALLY PARALLEL TO SAID BASE, SAID PLATE BEING IN THERMAL CONTACT WITH SAID SECOND FACE, AND MEANS CONNECTING SAID CIRCUIT COMPONENT AND THE FIRST AND SECOND FACES OF SAID THERMOSENSITIVE SUPPORT TO SAID ELECTRIC CURRENT CONDUCTORS, SAID FIRST FACE BEING COUPLED TO THE AMBIENT TEMPERATURE THROUGH A FIRST THERMAL RESISTANCE, SAID SECOND FACE BEING COUPLED TO THE AMBIENT TEMPERATURE THROUGH A SECOND THERMAL RESISTANCE, SAID FIRST THERMAL RESISTANCE BEING SUBSTANTIALLY LARGER THAN SAID SECOND THERMAL RESISTANCE. 